/*
 * Copyright (C) 2011 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.collect;

import static com.google.common.collect.BoundType.CLOSED;
import static com.google.common.collect.BoundType.OPEN;

import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.collect.Multiset.Entry;
import com.google.j2objc.annotations.Weak;

import java.util.Comparator;
import java.util.Iterator;
import java.util.NavigableSet;
import java.util.NoSuchElementException;
import java.util.SortedSet;
import javax.annotation.CheckForNull;

import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Provides static utility methods for creating and working with {@link SortedMultiset} instances.
 *
 * @author Louis Wasserman
 */
@GwtCompatible(emulated = true)
@ElementTypesAreNonnullByDefault
final class SortedMultisets
{
    private SortedMultisets()
    {
    }

    /**
     * A skeleton implementation for {@link SortedMultiset#elementSet}.
     */
    @SuppressWarnings("JdkObsolete") // TODO(b/6160855): Switch GWT emulations to NavigableSet.
    static class ElementSet<E extends @Nullable Object> extends Multisets.ElementSet<E>
            implements SortedSet<E>
    {
        @Weak
        private final SortedMultiset<E> multiset;

        ElementSet(SortedMultiset<E> multiset)
        {
            this.multiset = multiset;
        }

        @Override
        final SortedMultiset<E> multiset()
        {
            return multiset;
        }

        @Override
        public Iterator<E> iterator()
        {
            return Multisets.elementIterator(multiset().entrySet().iterator());
        }

        @Override
        public Comparator<? super E> comparator()
        {
            return multiset().comparator();
        }

        @Override
        public SortedSet<E> subSet(@ParametricNullness E fromElement, @ParametricNullness E toElement)
        {
            return multiset().subMultiset(fromElement, CLOSED, toElement, OPEN).elementSet();
        }

        @Override
        public SortedSet<E> headSet(@ParametricNullness E toElement)
        {
            return multiset().headMultiset(toElement, OPEN).elementSet();
        }

        @Override
        public SortedSet<E> tailSet(@ParametricNullness E fromElement)
        {
            return multiset().tailMultiset(fromElement, CLOSED).elementSet();
        }

        @Override
        @ParametricNullness
        public E first()
        {
            return getElementOrThrow(multiset().firstEntry());
        }

        @Override
        @ParametricNullness
        public E last()
        {
            return getElementOrThrow(multiset().lastEntry());
        }
    }

    /**
     * A skeleton navigable implementation for {@link SortedMultiset#elementSet}.
     */
    @GwtIncompatible // Navigable
    static class NavigableElementSet<E extends @Nullable Object> extends ElementSet<E>
            implements NavigableSet<E>
    {
        NavigableElementSet(SortedMultiset<E> multiset)
        {
            super(multiset);
        }

        @Override
        @CheckForNull
        public E lower(@ParametricNullness E e)
        {
            return getElementOrNull(multiset().headMultiset(e, OPEN).lastEntry());
        }

        @Override
        @CheckForNull
        public E floor(@ParametricNullness E e)
        {
            return getElementOrNull(multiset().headMultiset(e, CLOSED).lastEntry());
        }

        @Override
        @CheckForNull
        public E ceiling(@ParametricNullness E e)
        {
            return getElementOrNull(multiset().tailMultiset(e, CLOSED).firstEntry());
        }

        @Override
        @CheckForNull
        public E higher(@ParametricNullness E e)
        {
            return getElementOrNull(multiset().tailMultiset(e, OPEN).firstEntry());
        }

        @Override
        public NavigableSet<E> descendingSet()
        {
            return new NavigableElementSet<>(multiset().descendingMultiset());
        }

        @Override
        public Iterator<E> descendingIterator()
        {
            return descendingSet().iterator();
        }

        @Override
        @CheckForNull
        public E pollFirst()
        {
            return getElementOrNull(multiset().pollFirstEntry());
        }

        @Override
        @CheckForNull
        public E pollLast()
        {
            return getElementOrNull(multiset().pollLastEntry());
        }

        @Override
        public NavigableSet<E> subSet(
                @ParametricNullness E fromElement,
                boolean fromInclusive,
                @ParametricNullness E toElement,
                boolean toInclusive)
        {
            return new NavigableElementSet<>(
                    multiset()
                            .subMultiset(
                                    fromElement, BoundType.forBoolean(fromInclusive),
                                    toElement, BoundType.forBoolean(toInclusive)));
        }

        @Override
        public NavigableSet<E> headSet(@ParametricNullness E toElement, boolean inclusive)
        {
            return new NavigableElementSet<>(
                    multiset().headMultiset(toElement, BoundType.forBoolean(inclusive)));
        }

        @Override
        public NavigableSet<E> tailSet(@ParametricNullness E fromElement, boolean inclusive)
        {
            return new NavigableElementSet<>(
                    multiset().tailMultiset(fromElement, BoundType.forBoolean(inclusive)));
        }
    }

    private static <E extends @Nullable Object> E getElementOrThrow(@CheckForNull Entry<E> entry)
    {
        if (entry == null)
        {
            throw new NoSuchElementException();
        }
        return entry.getElement();
    }

    @CheckForNull
    private static <E extends @Nullable Object> E getElementOrNull(@CheckForNull Entry<E> entry)
    {
        return (entry == null) ? null : entry.getElement();
    }
}
